Fuel injectors are today used in many engines, for example in diesel engines used in trucks and off-highway equipment. The recent efforts to reduce engine emissions have focused on, among other things, a more complete combustion of the air-fuel mixture in the engine cylinders. This, in turn, is facilitated by pressurizing the fuel in the fuel injectors to a very high level, for example 207 MPa (30,000 p.s.i). Because of the high pressures, passages in the fuel injector must be carefully designed so that structural failures are avoided. Intersecting passages pose a particular problem owing to the possibility of hoop stresses in the passages being additive, thereby further increasing the possibility of fatigue cracking.
One type of fuel injector utilizes a valving mechanism comprising a high-pressure spill valve and a direct operated check (DOC) valve wherein the former is operated to circulate fuel through the injector for cooling, to control injection pressure and to reduce the back pressure exerted by the injector plunger on the camshaft following injection.